The invention relates generally to turbochargers, and more specifically, to control of turbochargers.
Conventionally, turbochargers are operably connected to an internal combustion engine in which exhaust gas from the engine is utilized to increase the pressure of intake air above ambient to the engine. Typically, the turbocharger includes a shaft, a driving turbine or expander attached at one end of shaft, and a compressor attached to the other end of the shaft. The expander is attached to the engine to receive exhaust gases from the engine and the compressor is attached to an air intake manifold of the engine.
During operation, the expander receives exhaust gas which causes the shaft to rotate, which in turn, causes the compressor to rotate and supply air to the air intake manifold of the engine at an increased pressure, i.e., at a pressure greater than ambient air pressure.
The turbochargers used to boost the power of both gasoline and diesel engines are typically uncontrolled (open loop) devices that impose performance constraints on both the turbocharger and the engine it boosts.
Some turbocharger control systems have incorporated mechanical waste gates and moveable guide vanes which physically reduce the driving energy of the exhaust on the turbine in some operating conditions. However, these devices have durability problems associated with their use because of the hostile environment in which they must operate (e.g., heat and vibration). For example, they may require lubrication, bearings and/or seals subject to failure in this hostile environment.
More recently, incorporation of a separate electric motor/alternator connected to the shaft to modulate and increase the rotational speed of the shaft in a continuous manner relative to and in response to the speed of the engine, to increase the rotational speed of the shaft to overcome “turbo lag” (i.e., the short period of time after increased power demand is first sensed until the rotary compressor driven by the exhaust gas turbine reaches its full power capacity), and also to extract electrical energy from the exhaust gas has been utilized. However, this approach is still technically immature.
Thus, there is still a need for a simple, robust control mechanism for tailoring the turbocharging of a gasoline engine or diesel engine, of a diesel electric locomotive for example, to increase engine performance and reliability.